1. Field of the Invention
The present invention relates to a toe-piece for binding a boot on a gliding board.
2. Description of Background
A number of toe-pieces incorporate a mechanism for lateral release of the boot, associated with the rotation of two wings. The two wings are biased by a spring to tightly grip the front of the boot to thereby retain it in place on the ski, or other gliding board, during use. As soon as a lateral threshold force is exerted on the front of the boot, a wing opens, thereby releasing the boot. This mechanism thereby ensures the safety of the skier in the event of a fall. The mechanism is typically adjustable so that the value of the lateral threshold force can be set to the specific characteristics of the skier.
Some toe-pieces of the aforementioned type further incorporate a compensation mechanism for modifying the release value during alpine skiing. For example, if the ski flexes, the front of the boot presses on a lever, displacing a support zone of the spring of the lateral release mechanism. This offset then modifies the stiffness of the spring while maintaining the tight grip of the wings on the front of the boot. This displacement causes a change in the lateral threshold release force. Typically, this action causes the threshold force to be lessened. During flexion, the front end of the boot is still clamped in the jaws. However, the lateral release value is lower, which makes it possible to release the boot with less lateral force. Such a toe-piece is described, for example, in U.S. Pat. No. 4,516,792.
With a toe-piece of the aforementioned type, the wings are continually in contact with the boot, when the boot is positioned between the toe-piece and the heel-piece. The compensation mechanism does not have any configuration in which the wings do not clamp the front of the boot. The only way to release the front of the boot is to trigger the mechanism by exerting a lateral force or to manually actuate the heel-piece, which makes it possible to move the boot backward to disengage it from the toe-piece. The actuation of the compensation mechanism does not make it possible to release the front of the boot but only reduces the lateral release threshold force value.
Other toe-pieces have two front boot-retaining devices. The first device is provided for the descent and comprises two pivotable wings cooperating with a lateral release mechanism, such device being similar to that described above. It comprises a spring, a first end of which is connected to the wings and a second end of which is supported on the frame of the toe-piece. The second front boot-retaining device of the toe-piece is provided for the ascent and comprises two pivotable points designed to cooperate with the front of the boot to enable the boot to rotate about a transverse axis defined by the alignment of these two points. For example, the document EP-A-2 626 116 discloses a toe-piece associating two front retaining devices, such that the release mechanism acts on the wings and on the points. This construction is characterized in that the stiffness of the spring of the release mechanism remains almost unchanged, whether the toe-piece is in the descent configuration or in the ascent configuration. It follows that when the toe-piece is in the ascent configuration, the release mechanism exerts a substantial force on the points to bring them closer together, this force corresponding substantially to the force exerted by the jaws in the descent configuration. This force is directly exerted on the front of the boot, which can cause wear of the boot in the area of the interface, on the one hand, and disturbance of the rotation of the boot about the hinge axis. Indeed, the greater the force exerted by the points, the more friction is generated during rotation of the boot. It is therefore desirable for the force exerted by the points on the boot to be the lowest to facilitate rotation of the boot about the transverse hinge axis. Conversely, it is necessary to maintain sufficient clamping force on the boot by the wings in the descent configuration. The previously proposed solution does not make it possible to differentiate the clamping force on the front of the boot between the descent configuration and the ascent configuration.